Block copolymers prepared from a conjugated diene and styrene suffer from the drawback that they lack good elastomeric properties at elevated temperatures. This is a serious deficiency in view of the expanding need for synthetic rubbers that can be utilized at high temperatures, as for example, hoses, belts, and gaskets used under the hood of an automobile. Previously, it has been demonstrated that block copolymers capable of withstanding higher temperatures can be obtained if the non-elastomeric polystyrene blocks are replaced with blocks of poly(alpha-methylstyrene). See U.S. Pat. No. 3,825,623.
Although U.S. Pat No. 3,294,768 contains broad teachings in regard to forming random copolymers of conjugated dienes and certain monovinylarenes, that patent in column 5, lines 7-10, indicates that the process is not applicable to monovinylarenes having a substituent on the alpha carbon atom.
An object of the present invention is to provide a method for producing random copolymers of conjugated dienes and alpha-methylstyrenes.
A further object of the present invention is to provide copolymers of conjugated dienes and alpha-methylstyrenes.
Still another object of this invention is to provide copolymers of conjugated dienes and alpha-methylstyrene that have unexpectedly broad molecular weight distribution.
Other aspects, objects, and advantages of the present invention will be apparent from the following description and examples.
In accordance with the present invention, random copolymers of at least one conjugated diene and at least one alpha-methylstyrene type monomer are produced by the solution polymerization of those monomers in the presence of an organolithium initiator and at least one of selected alkali metal organic compounds.